1. Field of Invention
This invention pertains to a method for making carbon or graphite filaments from pitch. Such filaments have utility in reinforcing plastic materials. Because the filaments can have high tensile strength and stiffness their addition to thermosetting or thermoplastic materials substantially enhance the resulting physical properties of the reinforced composite. The reinforced composite has many utilities; some of which are fan blades for turbine engines, golf shafts and tennis rackets. Much of the history of preparing such filaments, their physical properties, the preparation of composites containing the fibers, their influence on properties of composites and numerous end uses for such composites is disclosed in the pamphlet, CARBON FIBERS, Design Engineering Series, Morgan-Grampian (Publishers) Ltd., England.
2. Description of the Prior Art
U.S. Pat. No. 3,716,607, issued Feb. 13, 1973, discloses a method for the production of carbon fibers from various organic substances. The method involves heating the organic substance, forming the desired shape, oxidizing the formed shape and then carbonizing the oxidized shape.
U.S. Pat. No. 3,552,922, issued Jan. 5, 1971, discloses a method for the production of carbon fibers from petroleum acid sludge. This method involves a two-step distillation of the sludge, melt spinning the distilled material, coating the melt spun material with a surface modifying agent, treating the modified coated melt spun material with an oiling agent and carbonizing the oiled material.
U.S. Pat. No. 3,629,379, issued Dec. 21, 1971, discloses a method for producing carbon filaments from a pitch containing a carbon content of 91 to 96.5 weight percent and mean molecular weight of from 400 to 2000. Described are treatments for converting pitches having other than the aforementioned carbon content and molecular weight into pitches having the desired characteristics.
U.S. Pat. No. 3,392,216, issued July 9, 1968, discloses a method for producing carbon filaments from organic substances. The method involves heating the organic substance, shaping the heated substance, oxidizing the shaped substance and then carbonizing the oxidized substance.
The foregoing patents relate to the production of carbon fibers whereas U.S. Pat. No. 3,448,185, issued June 3, 1969, is directed towards a method of melt spinning of filaments. The method, in part, involves extruding molten fiber forming polymeric material through a spinneret vertically upward through a layer of liquid metal that is in direct contact with the spinneret. Examples of the polymeric materials are polypropylene and nylon-6; the metal used is one having a freezing point lower than the boiling point of water. However, one of the problems to date is the inability to form a continuous carbon or graphite filament from pitch. A continuous carbon or graphite filament from an already formed filament of polyacrylonitrile is feasible because the heat treatment is applied to an existing filament rather than a pre-filament. Also the prior art contains processing steps, such as oxidizing, which present invention does not. Elimination of such step results in economic savings and enhances the ease of manufacturing.